This invention relates to inkjet printheads and more particularly to an apparatus and method of electrically and fluidically coupling an ink-ejecting die to a substrate.
Various types of inkjet printers exist today offering a range of printing speeds, printing colors, and printing quality. Modern inkjet printers are capable of producing photographic-quality images and are generally less expensive than conventional laser-type printers because the printing mechanism is less expensive to produce. Additionally, thermal inkjet printers are quiet (as compared to conventional impact printers) because there is no mechanical impact during the formation of the image other than the deposition of ink onto the printing medium. Thermal inkjet printers, a type of inkjet printer, typically have a large number of individual ink-ejecting nozzles (orifices) disposed in a printhead. The nozzles are spatially positioned and are facing the printing medium. Beneath each nozzle is a heater resistor that thermally agitates the ink when an electrical pulse energizes the heater resistor. Ink residing above the heater resistor is ejected through the nozzle and towards the printing medium as a result of the electrical pulse. Concurrently, the printhead traverses the surface of the printing medium with the nozzles ejecting ink onto the printing medium. For high-speed printers, however, an array of printheads may be stationary relative to the printing medium while motion is imparted to the printing medium.
As ink is ejected from the printhead, the ink droplets strike the printing medium and then dry forming xe2x80x9cdotsxe2x80x9d of ink that, when viewed together, create a printed image. Most thermal inkjet printing systems are constructed with a permanent printer body and a disposable or semi-disposable printhead. The printhead includes a semiconductor die (hence forth referred to as a die) and a supporting substrate. Ink is typically supplied to the printhead from an ink reservoir formed within the printhead or from an ink reservoir attached to the printer. The latter configuration allows the printer to operate over an extended period of time prior to having the ink replenished.
In a conventional printhead, a die having heater resistors and accompanying ink-ejecting nozzles is fluidically and electrically coupled to a substrate. The fluidic coupling of the die may be achieved by attaching the die to the substrate wherein ink flows to the heater resistors (disposed in the die) from the edge of the die or from the center of the die. In either configuration, however, the ink reaches the heater resistors and is available to be ejected onto the printing medium. Electrical connections (interconnects) are also made between the die and the substrate.
Electrically coupling the die to the substrate requires forming an interconnect through which the printing instructions are supplied to the die. U.S. Pat. No. 4,940,413 illustrates such an interconnect. Here, a high density electrical interconnect that enables a large number of traces to be interconnected together in a small space is used to couple the die to a substrate. The electrical coupling of a die to the substrate as performed in inkjet technology, and as illustrated in the aforementioned patent, is sufficiently more complicated than electrically coupling a die to a substrate as commonly performed in conventional integrated circuit packaging. For example, the interconnects must be isolated from ink being ejected from the die due to the potential corrosiveness of ink. Additionally, certain constituents of the ink may be conductive thus causing electrical shorting of the interconnects. Secondly, the interconnects are exposed to continuous vibration and physical contact by the printer. The vibration is created, in part, from the traversing movement of the printhead relative to the printing medium whereas the physical contact between the printhead and the printer occurs during the cleaning cycle of the die. The cleaning cycle involves periodically passing a wiper across the die which removes ink residue and other particles that may degrade printing performance. In contrast, die used in conventional integrate circuit packaging is completely contained within the xe2x80x9cpackagexe2x80x9d and is isolated from an object, such as a wiper, contacting its surface. Thirdly, the interconnects are exposed to a wide range of temperatures stemming from the printing demands of the computer system. These temperatures result, in part, from the electrical excitation of the heater resisters. Consequently, the temperature of the die may rise sharply followed by an immediate cooling period. Thermal cycling of the die as such may fatigue the electrical interconnects causing them to break.
Although many attempts have been made, and indeed are ongoing, to resolve challenges previously described in electrically coupling the die to the pen body, there still remains a need for an improved printhead. An improved printhead as such would consist of electrical interconnects that are isolated from the ink and cleaning mechanism of the printer, electrical interconnects that are tolerant of rapid temperature changes, and an ink ejecting die that would operate in close proximity of the printing medium.
A print cartridge comprising an ink-ejecting die, the ink-ejecting die further comprises a substrate having at least an opposing upper and lower surface and a thin film stack disposed on the upper surface. At least one edge of the upper surface is beveled wherein a lower portion of the bevel is below an upper portion of the bevel. A conductive material trace is disposed on top of at least a portion of the upper surface and thin film stack. The conductive material trace extends from the upper surface and towards the lower portion of the bevel. An electrical conductor is coupled to the conductive material trace at a predetermined location below said upper portion of said bevel. Printing instruction and power is supplied to the ink-ejecting die through the electrical conductor.